1. Technical Field
The present disclosure relates generally to measurement apparatuses and methods and, more particularly, to the qualitative and quantitative mapping of ionic diffusion, interfacial electrochemical process, and electrochemical activity in solids using scanning probe microscopy and related methods on the nanometer scale.
2. Related Art
Solid-state energy storage systems based on intercalation and reconstitution chemistries are key components of multiple energy technologies. For example, the electrochemical energy storage systems based on Lithium (Li)-insertion and reconstitution chemistries are a vital aspect of future energy technologies for implementation in areas such as mobile devices, electric and hybrid cars, and solar and wind power technologies. Similarly, polymeric, oxide, and other fuel cells form the basis of multiple power sources. Metal-air batteries are being developed as a high energy density storage systems rivaling traditional fossil fuels. Equally important are applications of ionic solids in information technologies, for applications such as memristive and electroresistive memories and logic devices. However, the capability for probing ionic transport on the nanometer scale remains a key challenge for the development and optimization of energy storage and generation systems, such as batteries, fuel cells, and electroresistive and memristive devices and precludes knowledge-based strategies for device development and optimization.
Existing solid-state electrochemical characterization methods for probing ionic motion typically utilize slow and large scale ion-conducting electrodes, thus limiting studies of ion transport to a scale of approximately ten micrometers or greater. This scale of resolution is well above nanoscale level necessary to map intercalation, chemical reactions, strain, charge, and ion transport at the level of single grain boundaries and dislocations in the electrodes. At the same time, techniques based on direct electronic current detection are sensitive to stray electronic currents and (for AC methods) stray capacitances, limiting information on ion motion. As a result of the absence of microscopic techniques for probing ionic motion and electrochemical reactivity, the fundamental mechanisms underpinning ionic process in solids ranging from batteries to fuel cells to electroresistive materials and devices remained largely unexplored.
Scanning probe microscopy (SPM) based techniques now provide high resolution imaging of various material properties of host compounds. Substantial efforts have been made to characterize the properties of electrochemically active storage materials at the nanoscale level using SPM based techniques. However, the application of SPM techniques for probing local ion and electron transport and electrochemical kinetics at various length scales of electrochemical systems, from micron-scale grain assembly, to the sub-micron grain, and the nanometer scale of individual structural and morphological defects, has been limited because of the well known limits on current detection. Further, standard current-based electrochemical methods have proven to be time consuming, and require protective atmospheres or in-situ operation, and offer limited or indirect information on electrochemical properties. Accordingly, these techniques are inadequate for a thorough and complete characterization of the local ionic properties of electrochemically active storage materials.